1. Field of the Invention
The present invention relates to a heat sink cooling system for an integrated circuit package in an enclosed computer system.
2. Description of Related Art
Integrated circuits (ICs) are typically housed within a plastic or ceramic package. The packages have leads or surface pads that are soldered to a printed circuit board. The circuit board and package are often located within a computer chassis which contains a fan that removes the heat generated by the IC.
It is desirable to have a high rate of heat transfer from the IC package in order to maintain the junction temperatures of the integrated circuit within safe operating limits. Excessive IC junction temperatures may affect the performance of the circuit and cause a permanent degradation of the IC. Heat sinks are sometimes mounted to the top surface of the package housing to increase the thermal performance of the package. Conventional heat sinks typically have a plurality of fins that extend from a bottom base portion. The fins increase the surface area of the heat sink and the heat transfer rate of the package.
Microprocessors are a type of IC which often require a heat sink. For high performance microprocessors employed in an enclosed computer system, a high heat transfer rate is particularly important since the interior operating environment of typical computers is 10.degree. C. to 25.degree. C. above that of the air exterior to the enclosed computer system.
Several methods have been employed for cooling such high performance microprocessors. A common method of cooling such a microprocessor is by the use of a fan heat sink, in which an axial fan is attached to the heat sink atop the microprocessor in order to blow air across the heat sink to remove the heat dissipated by the microprocessor. To date, the best fan heat sinks are not thermally efficient enough to cool the higher powered new microprocessors.
One method of increasing the fan heat sink's efficiency, or lowering its thermal resistance, is to increase the speed of rotation of the fan prop, thereby forcing more air through the heat sink. The problem with this method is that at higher speeds of rotation, the fan consumes more power, further heating the fan motor bearings. Reliability of the fan heat sinks is a key concern for these high performance microprocessors. One failure mechanism of these small fans is a breakdown of the lubrication used in the bearings, which results at higher operating temperatures. Fan heat sinks have a drawback that they often require a system fan to move the heated air dissipated by the fan heat sink and to prevent recirculation of the heated air back to the fan heat sink.
Additionally, fan heat sinks have the drawback of having to operate in the elevated-temperature environment of the enclosed computer system. Subsequently, the fan heat sinks can encounter reliability problems due to operation at the elevated temperatures. Fan heat sinks also pose assembling problems since both a heat sink and a fan must be attached to each microprocessor.
Another approach is the use of passive heat sinks in combination with an axial system fan, but the large surface area requirements result in heat sink volumes that are too large for the typical computer chassis design.
Another approach involves the use of a liquid coolant to move the dissipated heat away from the microprocessor. Liquid cooling, however, is the least desirable and most expensive approach.
Accordingly, it would be advantageous to provide a reliable heat sink cooling system design. It would also be advantageous to provide a heat sink design which physically decouples the air mover (fan) from the heat sink.
It would also be advantageous to provide a cheap, easily constructed heat sink to efficiently dissipate the heat generated by the microprocessors.